Abstracts

Celia Escamilla (MCTP)

cescamilla@mctp.mx

Título: Precision cosmology of dark energy

Cosmology in the past twenty years has made the transition to precision cosmology. Because of the intrinsic nature of studying the universe and the sheer amount of data available now and coming soon, the way to meet this challenge is by developing suitable and specific statistical techniques. We will outline in this talk some open challenges and discuss some specific examples about dark energy using SNe Ia and BAO observational data within the framework of parameterisation representations.

Marcelo Salgado (ICN-UNAM)

marcelo@nucleares.unam.mx

Título: Black holes in f(R) gravity: scalar-hair or absence thereof

We discuss the conditions under which BH’s with trivial (i.e. constant) Ricci scalar exist in f(R) gravity and show that such BH’s are identical to the corresponding BH’s existing in GR except for a redefinition of the cosmological and the gravitational constants. We then focus on static and spherically symmetric spacetimes and provide the equations and regularity conditions required for the existence of spherically symmetric BH’s.Using several specific f(R) models we provide analytical and numerical evidence for the absence of geometric scalar hair in asymptotically flat (AF) spacetimes. The analytical evidence consists in the implementation of the no-hair theorem(s) that exist in the so called Einstein-Higgs system via a conformal transformation (i.e. using the Einstein frame representation). When the theorems do not apply or the use of the Einstein frame is ill-defined for some of the f(R) models, we solve the equations numerically in the original (Jordan) frame, and show that BH’s solutions with non-trivial Ricci scalar in AF spacetimes seem to be absent, and the only ones that exist with a non trivial Ricci scalar have “exotic”asymptotics.

Most of the close encounters between main sequence stars and supermassive black holes (SMBH) take place well within the regime where general relativistic effects play an important role. These effects correspond to both the strong gravitational field that prevails in the vicinity of these objects and to the frame dragging generated by a rotating SMBH. In this talk, I will present the outcome of recent simulations of tidal disruption events performed in two steps: initially with a new relativistic SPH code followed by a fully relativistic, magneto-hydrodynamics, grid-based code. I will discuss in particular the role played by relativistic effects in determining the formation of a debris disc and subsequent accretion on to the central BH.

Juan Carlos Degollado (ICF-UNAM)

jcdegollado@ciencias.unam.mx

Título: Dynamical hairy black holes in General Relativity

The uniqueness theorems led to the conjecture that the outcome of gravitational collapse in the presence of any type of matter-energy is a Kerr-Newman black hole, solely described by mass, angular momentum and electric charge. An interesting point of view concerning the weak no-hair hypothesis arises in the context of an instability of the Kerr solution which is triggered by fields that can, potentially, form black hole hair. Recently, new solutions of the Einstein equations involving scalar fields around black holes that may form dynamically have been found. In this talk I will revisit some of the properties of these hairy black hole solutions and present in some detail a toy model that emulate its dynamical behaviour.

It is well known that noncommutativity is commonly used in theories of grand unifications like strings or loops, however its consequences in standard astrophysics it is not well understood. For those reasons, this paper is devoted to study the astrophysical consequences of noncommutativity, focusing in stellar dynamics and rotational curves of galaxies. We start exploring stars with incompressible and polytropic fluids respectively, with the addition of a noncommutative matter. In both cases, we propose an appropriate constriction based in the difference between a traditional and an anomalous behavior.

As a complement, we explore the rotation curves of galaxies assuming that the dark matter halo is a noncommutative fluid, obtaining a value of the free parameter through the analysis of twelve LSB galaxies; in this sense our results are compared with traditional models like Pseudoisothermal, Navarro-Frenk-White and Burkert.

As we are entering the era of precision cosmology, it is necessary to count on accurate cosmological predictions from any proposed model of dark matter. This is the case for scalar field dark matter models, also known as axion like DM. In this talk we present a novel approach to the cosmological evolution of scalar fields that eases their analytic and numerical analysis at the background and linear order of perturbations. We will also discuss new constraints on this type of models based on the internal dynamics of dwarf spheroidal galaxies.

I present the computation of the dark matter velocity dispersion tensor up to the third order in Lagrangian perturbation theory. As an application, corrections to the matter power spectrum are calculated. Due to the presence of velocity dispersions, there exist a free-streaming scale that suppresses the whole 1-loop power spectrum; and as a consequence of nonlinear evolution, this scale is shifted toward larger scales, wiping out more structure than the expected in linear theory.

Pedro Carrilho (Queen Mary)

Título: Evolution of the curvature perturbation in the presence of vectors and tensors

We derive the evolution equations for the second order curvature perturbation for different definitions of that gauge invariant quantity, arising from different splits of the spatial metric. The results are valid at all scales and include all contributions from scalar, vector and tensor perturbations, as well as anisotropic stress, with all our results written purely in terms of gauge invariant quantities. In the large scale approximation, we find that a conserved quantity exists only if, in addition to the non-adiabatic pressure, the transverse traceless part of the anisotropic stress tensor is also negligible. We also find that the version of the gauge invariant curvature perturbation which is exactly conserved is the one defined with the determinant of the spatial part of the inverse metric, which is in turn related to the perturbation to the extrinsic curvature of comoving hypersurfaces.